IsOTOPIC CHARACTERIzATION OF sNOW, ICE AND GLACIAL mELT IN THE WEsTERN HImALAYAs, INDIA
4.4. Isotopic Composition of meltwater
Fig. 4 shows a δ2H vs δ18o plot for the meteoric water line developed for the meltwater of Gangotri Glacier at the Gomukh site and the best fit line is δ2H = 9.4 ± 0.7 δ18o + 37.5 ± 9.7, R2 = 0.96, n = 16 (2004–2005), which is consistent with lMWl of higher Himalayan snow and glacier with a slope of 8.7 and intercept of 29.9 [3].
the slope and intercept of the meltwater for the study region is similar to that reported earlier by Hren et al. [15], a slope of 10 and intercept of 39 for the stream water of the middle yarlung region and Zhou et al. [33], a slope of 10.4 and intercept of 41.4 for the snow pack at the altitude of 4860 m of Qilian Mts glacier. the three main post deposition processes of snow evaporation, melting and refreezing may modify the slope of the meteoric water line but do not cause an increase. evaporation and refreezing result in a slope decrease and melting has no clear impact on it [34, 35]. the high d-excess reveals that the source of moisture is western disturbances.
5. conclusIons
the results reveal that the source of precipitation during the ablation period is local moisture and sW summer monsoon.the high d value of snow, ice and glacial
FIG. 4. δ2H versus δ18O of meltwater (monthly weighted) during the ablation period 2004 and 2005.
δ2H = 9.4 δ18O + 37.5 r2= 0.96
δ2H= 8.2 δ18O + 10.3 (GMWL)
-160 -140 -120 -100 -80 -60 -40
-20 -18 -16 -14 -12 -10
δ2H (‰) δ18O (‰)
Rai et al.
melt reveals the source of moisture is western disturbances. the temporal variation in the isotopic composition of meltwater at gomukh is due to the melting of snow and ice at different altitudes and with an increase in air temperature. the meltwa-ter represents the integrated isotopic signature of snow and ice of different altitudes.
the abrupt change in isotopic signature in meltwater is due to the contribution from the sW monsoon to stream discharge as surface runoff. the present study reveals that stable isotopes are very useful in segregating the different components of stream dis-charge near the snout while conventional techniques have limitations. the long term data of δ18o of the river near the snout would be useful to study the impact of climate change on the melting of Himalayan glaciers.
ACkNOWLEDGEmENTs
the present work is part of the project sponsored by dst, new delhi. there-fore, the authors are thankful to DST for providing the financial assistance to carry out this study. the authors are grateful to the director, nIH, roorkee for providing the necessary help and permission to carry out this present work. sincere thanks are also due to Shri Y.S. Rawat, Project Officer, for extending his assistance in preparing this manuscript.
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